In recent years, in order to heighten the performance and safety of secondary batteries and electrochemical devices including capacitors, many studies have been made to use novel electrolytes in place of electrolytes which have hitherto been used
As such electrolytes, in general, there have so far been used liquid electrolytes wherein an ionic compound is dissolved in an organic solvent which is electrochemically comparatively stable (see, for example, Non-patent Document 1). However in this case, there has been pointed out that since there is a liquid having fluidity inside the electrochemical device, when the device was used for a long time, when the device was heated from the outside by a certain reason or when the device was physically destroyed due to the breakdown of some instrument, there is a possibility that the electrolyte liquid leaks from the inside of the electrochemical device to the outside.
In order to prevent the leak of the electrolyte liquid and further heighten safety, many studies have so far been made to use gel electrolytes or polymer electrolytes in place of liquid electrolytes which have hitherto been used (see, for example, Non-patent Document 1). However, even in this case, a danger has not been overcome that the gel electrolytes or polymer electrolytes, which are combustible, may be ignited or burnt at the time of heating.
As polymer electrolytes whose safety is further heightened, there have, for example, been known polymer electrolytes wherein a solid electrolyte such as lithium perchlorate is added to a polymer (see, for example, Patent Document 1). In the case, polyether-type polymers having high affinity to lithium cations are often used. Since ion conduction takes place by link with motion (relaxation) of the polymer chain, ion conductivity is low, and, thus, it can hardly be said that such polymer electrolytes, when used as electrochemical devices, are sufficient in performance. In order to overcome this, there is often a case where a high polar organic solvent such as acetonitrile or propylene carbonate is added, but, in the case, a danger of inflammation, ignition or combustion cannot be avoided.
For coping with problems like this, there have, in recent years, been reported studies on solid electrolytes wherein an ionic liquid as a novel electrolyte is solidified (see, for example, Patent Documents 2 and 3 and Non-patent Documents 2 and 3). Since ionic liquids are generally noninflammable, a danger of inflammation, ignition or combustion of the electrolyte is overcome, and, at the same time, since the ionic liquids are immobilized, the problem of leak of electrolyte liquids from electrochemical devices is also greatly improved. In these solid electrolytes, since an ionic liquid is mixed with an epoxy compound or methacrylate monomer or the like to be solidified through chemical crosslinking or polymerization, there has been a problem that the obtained solidified product no longer has thermoplasticity, and it is impossible to mold the product into any shape by thermoforming, solution casting, a printing method or a coating method. In the above, it is not meant that ionic liquids are actually solidified, and “solidifying” means a “confined” state or an “immobilized” state.
As thermoplastic polymer electrolytes, ones using a graft copolymer are considered. For example, there is disclosed in the comparative example of Patent Document 1 a polymer electrolyte using as an electrolyte lithium perchlorate, and as a polymer a graft copolymer wherein a polyethylene glycol chain is grafted onto a polyethylene. Therein, although when an ionic liquid is used in place of lithium perchlorate, comparatively high ion conductivity can be obtained, there is a problem that the mechanical strength of the polymer electrolyte is low and bleeding-out of the ionic liquid tends to occur, and, thus, there are problems that the polymer electrolyte is poor in stability of performance, stability of a long-period use, and handling properties.
On the other hand, in the fields of medical instruments, micro-machines, etc., need for miniature and lightweight actuators increases. Further, also in the fields of industrial robots, personal robots, etc., need for lightweight and flexible actuators increases.
It is said that since when an actuator is miniaturized, friction and viscosity become dominant than inertial force, a mechanism to convert energy into motion utilizing inertial force, as in motors and engines, is hard to use as an actuator for microminiature machines. As kinds of microminiature actuators in view of actuation mechanisms so far proposed, an electrostatic actuator, a piezoelectric actuator, an ultrasonic motor, a shape memory alloy actuator, etc. are known. An electrostatic actuator is one wherein a plate or rod as one of the electrodes is attracted to the counter electrode, and one wherein one of the electrodes is bent by applying a voltage of the order of 100 V between the electrode and the other counter electrode scores of μm apart from the former electrode is known. A piezoelectric actuator is one wherein a voltage of several V is applied to the piezoelectric element made of a ceramic such as barium titanate to make the element expand and contract, and one capable of controlling a displacement of the order of nm is known. As an ultrasonic motor, one to be driven by causing dislocation with a combination of ultrasonic oscillation generated by a piezoelectric element or the like and frictional force is known. A shape memory alloy actuator largely changes in shape in accordance with temperature, and is driven by changing temperature. However, these types of actuators have problems that since they are made of inorganic substance(s) such as metal(s) or ceramic(s), there is a limitation in softening and/or lightening thereof; and since they are complicated in structure, their miniaturization is not so easy; and so on.
As actuators capable of overcoming the above problems, polymer actuators draw attention recently. For example, polymer actuators utilizing change in the shape of hydrated polymer gels due to stimulation such as temperature change, pH change or application of electric field are devised (see, for example, Patent Document 4). However, since the change in shape of hydrated polymer gels due to various stimulations is generally very slow, and, further, the mechanical strength of hydrated polymer gels is low due to their not uniform crosslinking structure, further improvement is necessary for actually utilizing such a polymer actuator as an actuator.
In order to overcome the above problems, polymer actuators are devised which is composed of an ion-exchange polymer membrane and electrodes bonded to both surfaces thereof, and wherein an electric potential difference is applied to the ion-exchange polymer membrane to bend and deform the membrane (see, for example, Patent Document 5). However, since water is indispensable for actuation of the polymer actuators, there is a problem that the environment of actuation thereof is limited to a wet environment.
In order to overcome this problem, there is reported polymer actuators wherein two electrodes each consisting of an ionic liquid, a fluorine-containing crystalline polymer and single wall carbon nanotubes are stuck on both surfaces of a polymer electrolyte consisting of the ionic liquid and a fluorine-containing crystalline polymer (see, for example, Non-patent Document 4). Further, there is reported polymer actuators wherein two pieces of gold foil as an electrode are stuck on a polymer electrolyte prepared by mixing an ionic liquid, a monomer and a crosslinking agent and curing them (see, for example, Patent Document 6). However, as to the former, there is a problem that since fluorine-containing crystalline polymers are poor in liquid-retaining property of ionic liquids, the ionic liquid bleeds out from the polymer electrolyte. On the other hand, as to the latter, there is a problem that since the ionic liquid is immobilized by crosslinking, the polymer electrolyte is narrow in room of selection of shapes.    Patent Document 1: JP-A-2004-98199    Patent Document 2: JP-A-2004-281147    Patent Document 3: JP-A-2006-32237    Patent Document 4: Tokkai-sho 63-309252 (JP-A-1988-309252)    Patent Document 5: Tokkai-hei 4-275078 (JP-A-1992-275078)    Patent Document 6: JP-A-2005-51949    Non-patent Document 1: Denshi to ion no Kinoukagaku siriiz vol. 2, “Daiyoryo Denkinijuso Kyapasita no Saizensen”, Enu Tii Esu (Series of Chemistry of Function of Electrons and Ions Vol. 2, “Frontier of Large Capacity Electrical Double Layer Capacitor”, NTS    Non-patent Document 2: Journal of American Chemical Society, Vol. 127, page 4976, 2005    Non-patent Document 3: Journal of Physical Chemistry, Vol. 109, page 3886, 2005    Non-patent Document 4: Expected Materials for the Future, Vol. 5 No. 10, page 14, 2005